<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <input id="ipt" type="password"/>
    <button id="eyebtn">eye</button>
    <script>
        let ipt = document.querySelector('#ipt')
        let eyebtn = document.querySelector('#eyebtn')

        eyebtn.onclick = function(){
            if(ipt.type == 'text'){
                ipt.type = 'password'
            }
            else{
                ipt.type = 'text'
            }
        }
    </script>
</body>
</html>